02-19-2015, 09:04 AM
Well, I finally made all my tests, and it appeared the root cause was the USB 3.0 host controller.

Indeed whenever the external usb drive was connected to a USB port 2.0 or 3.0, it wasn't seen in the WINPE environment, till the USB 3.0 host controller was activated in the BIOS.
As soon as it was deactivated, then the cloning process worked like a charm, on both USB 2.0 & 3.0 ports.